my model is much bigger than the 3d and 0-1 space
Remember, size in the computer is a relative, mathematical construct (it's not real) Size becomes an issue when you are stressing the the limits of the math engine. examples: If you build a model of a cup and you have the scale very large, relative to the programs space you'll have a crazy time detailing it, likewise an intricate model of a ship built "very small" will give you fits. You are translating the mathematical construct in the computer to a reasonable size for mapping pixel information to parts.

You should try to work in those "units" that make sense for the object: cup in inches, ship in meters. It's all about your modelling space. Then use reasonable UV mapping for the object. (don't try to use a single UV map for an entire ship model) So it's all about the scaling, bounds, mapping....

Then this link might get you going?
https://www.blender.org/manual/editors/uv_image/texturing/unwrapping.html

Hope this helps.
Kevin